A rubber pressure-sensitive adhesive agent generally consists of a rubber ingredient of a main ingredient and a tackifier, and in addition it is appropriately blended with a softener, a filler or the like. The rubber ingredient and the tackifier are hydrophobic materials which are extremely low in solubility and miscibility toward water, and an adhesive patch for an external use on the skin using such a pressure-sensitive adhesive agent easily peel off when having a bath, making a kitchen work or sweating, and therefore, it is necessary to let it have a high adhesive force in advance.
Although it is better to increase the amount of a tackifier in order to improve an adhesive force and a tack force, it lacks affinity toward water due to a high hydrophobicity as described above, and a grass transition temperature (Tg) of the system increases, resulting to a hard pressure-sensitive adhesive feeling to give a strong pain when removing, and therefore, it becomes not preferable as an adhesive patch for an external use on the skin.
In the meantime, a pressure-sensitive adhesive which contains no tackifier is proposed in patent document 1. By blending a liquid rubber in stead of a tackifier, Tg is reduced because the entire system is plasticized, whereby it is possible to improve adhesiveness toward a subject. However, there is a tendency that a cohesive force is slightly deficient, and therefore, a poor long-term stability due to deformation by flowing, a cohesion destruction, occurrence of a residue of an adhesive mass, and the like do not satisfy a use feeling as an adhesive patch for an external use on the skin.
In addition, although in patent document 2 it is proposed that three of a solid rubber ingredient at ordinary temperature, a tackifier and a liquid rubber are contained in combination at a specific ratio, more tackifier is needed to secure tackiness when the solid rubber at ordinary temperature is A-B-A type copolymer, and therefore, it gives a hard pressure-sensitive feeling and removal feeling, whereby skin irritations such as rash are easily caused. Further, when rubber solid at ordinary temperature, which does not have a physical cross-linking point, is used, a residue of an adhesive mass and the like due to an insufficient cohesive force do not satisfy a use feeling as an adhesive patch for an external use on the skin.
Patent document 1: JP, 8-506127 A
Patent document 2: JP, A, 2002-69405